This invention relates to membrane structures for storage tanks for low-temperature liquified gases of the kind comprising side and bottom walls incorporating corrugated expansion joints.
Heretofore, various constructions for the membrane structure have been made employing corrugations for the purpose of absorbing strains caused by thermal movements. Among these is a membrane wall construction in which corrugated members are assembled in a square-lattice pattern to form a framework, and each of the square openings defined by this framework is closed and made liquid-tight by use of a thin plate. Normally, central portions of the thin plates, or central portions of the corrugated members are anchored to support walls by means of bolts, rivets, etc. However, prior art structures constructed as described above have the following disadvantages:
(1) Since the corrugated members or thin plate members are anchored, when a liquid to be stored is poured into the tank, upon thermal contraction of only a part of the bottom wall, the entire bottom wall or the broad sweep of its section cannot follow the contraction. Thus, deformation of the corrugations locally becomes large and can result in permanent deformation of the corrugations; in cases where the thermal strain cannot be absorbed by only the corrugations of that part of the bottom wall which is subjected to thermal contraction, the corrugations may be damaged.
(2) Since anchoring is generally made at a large number of points, the increase in the cost of construction is inevitable.
(3) An accidental leakage of the stored liquid through an anchoring point is also liable to occur.
Low-temperature storage tanks are generally made cylindrical in shape in order to economise in the use of materials and to withstand the pressure. Accordingly the bottom wall is circular in shape. In addition, since the inside of the cylindrical tank is exposed to an ultra-low temperature, a membrane structure having corrugations is often used for the inner side and bottom walls for the purpose of absorbing thermal strains.
In view of the aforementioned circumstance, tanks of the prior art have disadvantages in that matching the corrugations between a side wall and the bottom wall, is difficult, and if the bottom wall which is placed under the influence of the most severe thermal strain, is to be formed in such a way that the strain can be fully absorbed, then it is difficult to construct the junction in the vicinity of the boundary of the bottom wall where it is joined with the side wall. This inevitably results in a membrane structure in which strain concentration is liable to occur in the vicinity of that boundary. In such a case, there could arise a complex structurally strained state in the joint portion between the bottom and side walls.